Most printing systems use a standardized color scheme called SWOP. In this color scheme, halftone masks are developed for cyan (C), magenta (M), yellow (Y) and black (K) inks having printed solid optical densities of 1.33, 1.47, 1.0 and 1.6. This color scheme is consistent with the limitations of the standard offset lithographic printing process. Due to the fact that in this process the image is "split" several times during its transfer from printing plate to paper and due to the rheologic limitations placed on the ink by the process, higher printed solid optical densities are not achieved in the standard offset lithographic printing process.
In order to assure standardized results from different print sources, the printed solid optical densities described above have been standardized and standardized color schemes developed around these densities. Printed versions of original images having a higher color density than that available from the standard color printing schemes will have a narrower color gamut in the final printed version than in the original and the half-toning process will either truncate the higher color densities or compress the color gamut of the original into the color density range available with SWOP.
Such printing is not optimum. In order to reproduce photographs and other artwork with high fidelity, a higher printed solid optical density would be required. However, printing such higher optical densities requires additional printing steps.
Two systems utilizing additional printing steps are known. In one such system red(orange), blue (violet) and/or green inks are printed in addition to the standard CMY colors. This improves the color density possible for these colors (and mixed colors having a large proportion of the added colors) but is not effective to increase the color saturation for the entire range of colors.
A second system is based on printing the CMY colors more than once to achieve a thicker layer of ink and thus a higher color density for those portions of the image which require it. This system does give an improved color density, but requires printing each color twice. If process black is printed in addition to CMY a total of seven printing steps, one for black and two each for CMY, are required. This system is marketed by DuPont under the trade name Hypercolor.TM. Software.